The present invention relates to hydrostatic charge pumps and, more specifically, to a charge pump with two independent outlets that can satisfy the pressure requirements of both a charge circuit and an auxiliary circuit.
Hydraulic systems often use a common flow source to satisfy the flow requirements of both the charge and implement or auxiliary circuits. Yet, meeting the flow requirements of both circuits often is difficult. In one conventional arrangement, the charge pump supplies pressure first to the auxiliary circuit before sending pressure to the charge circuit. If the pump is unable to meet the requirements of both circuits, however, the low pressure levels of the charge circuit can cause the hydrostatic pump to fail. In other conventional arrangements, the charge pump provides pressure to the charge circuit first, followed by the auxiliary circuit. This arrangement, however, often causes the charge circuit pressure to rise and fall in relation to the auxiliary circuit pressure requirement, causing heavier loading on the hydrostatic pump and additional hydrostatic power losses.
U.S. Pat. No. 5,165,233 to Betz attempted to solve the problems in the prior art by the use of a charge pressure priority valve. Implementation of this valve, however, requires that the pressure at the charge pump outlet always be set for the auxiliary circuit. Although use of a priority valve prevents failure or damage to the hydrostatic pump, it is not without its shortcomings. Because of the pressure drop from the auxiliary circuit requirement to that of the charge circuit, there are considerable power losses associated with the use of a priority valve.
It is therefore a principal object of this invention to provide a charge pump that can satisfy the pressure requirements of both a charge circuit and an auxiliary circuit with a minimal of power loss.
A further object of this invention is to provide a charge pump that can satisfy the pressure requirements of both a charge circuit and an auxiliary circuit using two independent discharge outlets.
These and other objects will be apparent to those skilled in the art.